The present invention relates to a polymer film that is used in the manufacturing of future integrated circuits (xe2x80x9cIC""sxe2x80x9d) and, in particular, to methods of making a polymer film that will retain their structural integrity during and after exposure to processes involved in the fabrication of IC""s.
During the manufacturing of IC""s, multiple layers of films are deposited. Maintaining the compatibility and structural integrity of the different layers throughout the processes involved in finishing the IC is of vital importance. In addition to dielectric and conducting layers, its xe2x80x9cbarrier layerxe2x80x9d may include metals such as Ti, Ta, W, and Co and their nitrides and silicides, such as TiN, TaN, TaSixNy, TiSixNy, WNx, CoNx and CoSi Nx. Ta is currently the most useful barrier layer material for the fabrication of future IC""s that use copper as conductor. The xe2x80x9ccap layerxe2x80x9d normally consists of dielectric materials such as SiN, SiON, TEOS, SiyOx, FTEOS, SiCOH, and SiCH.
Poly (para-xylylene) (xe2x80x9cPPXxe2x80x9d) thin films, which have low dielectric constants (xe2x80x9c∈xe2x80x9d), are found in various forms. PPX thin film has the repeating unit of (xe2x80x94CX2xe2x80x94C6H4xe2x88x92nZnxe2x80x94X2Cxe2x80x94)N, where X and Z are the same or different and each is H or a halide; n=0 to 4, and N is an integer denoting the number of repeating units, ranging from at least 10 to preferably at least 20, and more preferably at least 50. These films are useful in the manufacturing of future IC""s for several reasons. PPX-F i.e. [(xe2x80x94CX2xe2x80x94C6H4xe2x88x92nZnxe2x80x94X2Cxe2x80x94)N, where X=F, Z=H, n=0, and N as defined above] films prepared from dimers have shown, through X-Ray Photo Spectroscopy (xe2x80x9cXPSxe2x80x9d), undetectable changes in chemical composition after annealing at 425xc2x0 to 450xc2x0 C. for two hours in a vacuum (Plano et al., MRS Symp. Proc., Vol 476, (1998)). In addition, using the bending beam technique, it has been shown that PPX-F films are dimensionally stable up to the same temperature range after the first thermal cycle (Ho et al., MRS Spring Meeting Proceeding, Section 06.9 (1999)). It is also known that PPX-F films adsorb less than 0.02-0.04% moisture at ambient temperatures.
Various attempts to integrate PPX-F thin films into IC""s using Cu Dual Damascene processes have failed (Wary et al., Proc. 2nd Intl. DUMIC (1996); Wary et al., Semiconductor Int""l, 19(6) (1996); Lu et al., J. Mater. Res., Vol. 14(1) (1999); Plano et al., MRS Symp. Proc., Vol 476, (1998)). None of the previous studies teaches processes or methods to make PPX-F films that pass the Ta compatibility test. A compatibility test uses a sample consisting of a thin (50 to 200 Angstrom) barrier or cap layer, such as Ta or SiC over a dielectric layer, such as PPX-F, on a silicon wafer. The sample is then subjected to increasing temperatures at different lengths of time and the structural integrity of the film layers is recorded. In the previous tests, the Ta barrier layer failed after the sample was annealed at 350xc2x0 C. for 30 minutes under inert conditions.
What is needed, therefore, is a method for integrating a PPX film into future IC""s that maintains the film""s stability and compatibility with other layers.
An object of the present invention is to provide a PPX film that is suitable for fabrication of IC""s using the Cu Dual Damascene process.
Another object is to provide processing methods that will make a PPX film that is compatible with barrier layer materials used in the manufacturing of future IC""s.
A further object is to provide processing methods that will make a PPX film that is compatible with cap layer materials used in the manufacturing of future IC""s.
Another object is to provide processing methods that will make a PPX film that remains stable at the high temperatures encountered in the manufacturing of future IC""s.
In one embodiment of the present invention, there is a polymer film suitable for the fabrication of future IC""s. It is preferably prepared by the process of polymerization of diradical intermediates under a vacuum with a low system-leakage-rate, or an inert atmosphere or both. The inert atmosphere is preferably devoid of free radical scavengers or compounds containing active hydrogen. In a specific embodiment, the diradical intermediate has the general structure e-CX2xe2x80x94Arxe2x80x94X2Cxe2x80x94e, where X=H or F, Ar is an aromatic diradical containing 6 to 30 carbons, and e is a free radical having an unpaired electron. In additional specific embodiments, the aromatic diradical is C6H4xe2x88x92nxe2x80x94Fn (where n=0 to 4), C10H6xe2x88x92nxe2x80x94Fn (where n=0 to 6), C12H8xe2x88x92nxe2x80x94Fn (where n=0 to 8), C14H8xe2x88x92nxe2x80x94Fn (where n=0 to 8), or C16H8xe2x88x92nxe2x80x94Fn (where n=0 to 8). In further specific embodiments, the repeat unit of the polymer is CH2xe2x80x94C6H4xe2x80x94H2C, CF2xe2x80x94C6H4xe2x80x94F2C, CF2xe2x80x94C6F4xe2x80x94F2C, CH2xe2x80x94C6F4xe2x80x94H2C, CF2xe2x80x94C6H2F2xe2x80x94CF2, or CF2xe2x80x94C6F4xe2x80x94H2C. In other preferred embodiments, the vacuum is lower than 100 mTorrs, and preferably below 30 mTorrs. In further specific embodiments, the system leakage rate is less than about 2 mTorrs per minute, preferably less than 0.4 mTorrs/minute. In another preferred embodiment, the polymer film has a melting temperature (xe2x80x9cTmxe2x80x9d) greater than its reversible crystal transformation temperature (xe2x80x9cT2xe2x80x9d), which is greater than its irreversible crystal transformation temperature (xe2x80x9cT1xe2x80x9d), which is greater than its glass transition temperature (xe2x80x9cTgxe2x80x9d). In an additional specific embodiment, the polymer film is a fluorinated or unfluorinated PPX film having a general structure of (xe2x80x94CX2xe2x80x94C6H4xe2x88x92nZnxe2x80x94X2Cxe2x80x94)N, where X=H or F, Z=H or F, n is an integer between 0 and 4, and N is the number of repeat units, greater than 10. Preferably, N is greater than 20 or 50 repeat units. In another embodiment, the PPX film is transparent and semicrystalline. In further specific embodiment, the PPX film is PPX-F, which has a repeating unit with the structure of CF2xe2x80x94C6H4xe2x80x94F2C.
Another preferred embodiment is a method for preparing the polymer films by polymerizing the diradical intermediates at temperatures at or below their melting temperatures and with a low feed rate. In specific embodiments for the preparation of PPX-F films, the temperature of the substrate is lower than xe2x88x9230xc2x0 C. and preferably below xe2x88x9235xc2x0 C. The feed rate may be lower than 1.0 mMol/minute and preferably below 0.05 mMol/minute. In a specific embodiment, the method uses diradical intermediates with the general structure exe2x80x94CX2xe2x80x94Arxe2x80x94X2Cxe2x80x94e, where X=H or F, Ar is an aromatic diradical containing 6 to 30 carbons, and e is a free radical having an unpaired electron. In additional specific embodiments, the aromatic diradical used is C6H4xe2x88x92nxe2x80x94Fn (where n=0 to 4), C10H6xe2x88x92nxe2x80x94Fn (where n=0 to 6), C12H8xe2x88x92nxe2x80x94Fn (where n=0 to 8), C14H8xe2x88x92nxe2x80x94Fn (where n=0 to 8), or C16H8xe2x88x92nxe2x80x94Fn (where n=0 to 8). In further specific embodiments, the repeat unit of the polymer created by the method is xe2x80x94CH2xe2x80x94C6H4xe2x80x94H2Cxe2x80x94, xe2x80x94CF2xe2x80x94C6H4xe2x80x94F2Cxe2x80x94, xe2x80x94CF2xe2x80x94C6F4xe2x80x94F2Cxe2x80x94, xe2x80x94CH2xe2x80x94C6F4xe2x80x94H2Cxe2x80x94, xe2x80x94CF2xe2x80x94C6H2F2xe2x80x94CF2xe2x80x94, or xe2x80x94CF2xe2x80x94C6F4xe2x80x94H2Cxe2x80x94. In other preferred embodiments, the vacuum utilized is lower than 100 mTorrs, and preferably below 30 mTorrs. In further specific embodiments, the system leakage rate is less than about 2 mTorrs per minute, preferably less than 0.4 mTorrs/minute. In another preferred embodiment, the polymer film produced by the method has a melting temperature (xe2x80x9cTmxe2x80x9d) greater than its reversible crystal transformation temperature (xe2x80x9cT2xe2x80x9d), which is greater than its irreversible crystal transformation temperature (xe2x80x9cT1xe2x80x9d), which is greater than its glass transition temperature (xe2x80x9cTgxe2x80x9d).
In an additional specific embodiment, the method generates a fluorinated or non-fluorinated PPX film having a general structure of (xe2x80x94CX2xe2x80x94C6H4xe2x88x92nZnxe2x80x94X2Cxe2x80x94)N, where X=H or F, Z=H or F, n is an integer between 0 and 4, and N is the number of repeat units, greater than 10. Preferably, N is greater than 20 or 50 repeat units. In another embodiment, the PPX film generated is transparent and semicrystalline. In further specific embodiment, the PPX film is PPX-F.
In an additional specific embodiment, the method also includes heating the polymer film under an inert atmosphere to a temperature ranging from 20xc2x0 to 50xc2x0 C. below T2 to 20xc2x0 to 50xc2x0 C. below Tm, holding the sample isothermally for 1 to 120 minutes, then cooling the sample at a rate ranging from 30xc2x0 to 100xc2x0 C./minute, to a temperature ranging from 20xc2x0 to 50xc2x0 C. below T2. Preferably, the sample is held isothermally for between 2 and 60 minutes and is cooled at a rate of 50xc2x0 to 100xc2x0 C./minute. In another embodiment, the method for preparing the films also includes annealing them at temperatures 30xc2x0 to 50xc2x0 C. above their Tg for 5 to 60 minutes. This annealing process may also be performed at a temperature above T1 and is ideally done between 15 to 30 minutes. In a further preferred embodiment, the polymer film is stabilized by annealing the film at a temperature equal to or higher than the maximum temperature the polymer will encounter during the fabrication of IC""s for 10 to 60 minutes, and preferably 30 to 60 minutes.
Additional preferred embodiments include an active matrix liquid crystal display (xe2x80x9cAMLCDxe2x80x9d) and a fiber optical device that include the stabilized polymer films described in this invention.
Broadly, the present invention pertains to processing methods of polymer films that exhibit at least an irreversible crystal transformation temperature (xe2x80x9cT1xe2x80x9d), a reversible crystal transformation temperature (xe2x80x9cT2xe2x80x9d) and a crystal melting temperature, Tm.
I. Structure and Characteristics of PPX Films
The polymer films of this invention have a general chemical structure of (xe2x80x94CX2xe2x80x94Arxe2x80x94X2Cxe2x80x94)N, where X=H or F and Ar is an aromatic moiety. Examples of the aromatic moiety, Ar, include, but are not limited to, the phenyl moiety, C6H4xe2x88x92nFn (n=0 to 4), including C6H4 and C6F4; the naphthenyl moiety, C10H6xe2x88x92nFn (n=0 to 6), including C10H6 and C10F6; the di-phenyl moiety, C12H8xe2x88x92nFn (n=0 to 8), including C6H2F2xe2x80x94C6H2F2 and C6F4xe2x80x94C6H4; the anthracenyl moiety, C12H8xe2x88x92nFn (n=0 to 8); the phenanthrenyl moiety, C14H8xe2x88x92nFn (n=0 to 8); the pyrenyl moiety, C16H8xe2x88x92nFn (n=0 to 8) and more complex combinations of the above moieties, including including C16H10xe2x88x92nFn (n=0 to 10). Isomers of various fluorine substitutions on the aromatic moieties are also included. Preferably, Ar is C6F4, C6H4, C10F6, or C6F4xe2x80x94C6F4.
In addition, all fluorinated or non-fluorinated PPX films that have a general structure of (xe2x80x94CX2xe2x80x94C6H4xe2x88x92nZnxe2x80x94X2Cxe2x80x94)N can be used in the processing conditions described in this invention. In these PPX films, X=H or a halide, Z=H or F, n=0 to 4, and N is the number of repeat units. N should be at least 10, preferably at least 20, and more preferably at least 50.
Any material with a low dielectric constant, such as a PPX film, has to possess several important attributes to be acceptable for integration into IC""s.
First, the dielectric should be compositionally and dimensionally stable. The structural integrity should remain intact after integration into the IC""s and throughout the fabrication processes. These processes include reactive ion etching (xe2x80x9cRIExe2x80x9d) or plasma patterning, stripping of photoresist, chemical vapor or physical vapor deposition (xe2x80x9cCVDxe2x80x9d or xe2x80x9cPVDxe2x80x9d) of barrier and cap materials, electroplating and annealing of copper and chemical mechanical polishing (xe2x80x9cCMPxe2x80x9d) of the copper. In addition, to maintain its electrical integrity after the IC fabrication, the dielectric should be free from contamination by barrier materials such as Ta.
Also, the dielectric should not cause the structural or chemical breakdown of a barrier or cap layer. No corrosive organic elements, particularly any that would cause interfacial corrosion, should diffuse into the barrier or cap material. In addition, the dielectric should have sufficient dimensional stability so that interfacial stress resulting from a Coefficient of Thermal Expansion (xe2x80x9cCTExe2x80x9d)-mismatch between the dielectric and barrier or cap layer would not induce structural failure during and after the manufacturing of the IC""s.
Finally, the interfaces of the dielectric and barrier or cap layers should be free from moisture, preventing the occurrence of ionic formation and/or migration when the IC""s are operated under electrical bias.
The PPX films can be prepared by polymerization of their corresponding reactive diradical intermediates via transport polymerization. (Lee, J., Macromol, et al., Sci-Rev. Macromol. Chem., C16(1) (1977-78)). Examples of the PPX films and their repeat units resulting from polymerization of the diradical intermediates include commercially available products, such as: PPX-N (xe2x80x94CH2xe2x80x94C6H4xe2x80x94CH2xe2x80x94); PPX-F (xe2x80x94CF2xe2x80x94C6H4xe2x80x94CF2xe2x80x94); and perfluoro PPX (xe2x80x94CF2xe2x80x94C6F4xe2x80x94CF2xe2x80x94).
In general, diradical intermediates can be prepared from pyrolysis of corresponding dimers according to the Gorham method (U.S. Pat. No. 3,342,754). They can also be prepared by pyrolysis of monomers and co-monomers (see U.S. patent application xe2x80x9cIntegration of Low xcex5 Thin Film and Ta Into Cu Dual Damascene,xe2x80x9d Ser. No. 09/795,217, the entire content of which is hereby incorporated by reference) under vacuum conditions or an inert atmosphere. The vacuum should be lower than about 100 mTorrs, preferably about 30 mTorrs. The vacuum system should also have an air or system leakage rate of less than about 2 mTorrs/minute, preferably about 0.4 mTorrs/minute. An inert atmosphere is an atmosphere that is devoid of free radical scavengers such as water and oxygen, or devoid of a compound containing an xe2x80x9cactive hydrogen,xe2x80x9d such as an xe2x80x94OH, xe2x80x94SH, or xe2x80x94RNH group.
The resultant PPX products can be transparent or opaque films or in powder form depending on processing conditions. Only continuous films can be useful for IC manufacturing applications. Opaque films which contain cracks or spherulites with crystal sizes even in sub-micrometer range are not useful for this invention. Transparent films can be in an amorphous or semicrystalline PPX phase. When its crystalline phase is less than 10 nm or lower, semicrystalline PPX films can be useful for the manufacturing of future IC""s. Amorphous PPX films consist of random polymer chain orientations, which will create equal interfacial stress in all directions, thus avoiding problems that are associated with semi-crystalline polymers. However, amorphous PPX films that consist of a regular chemical structure or repeating unit in their backbone structures can be re-crystallized into semicrystalline films. For example, these amorphous PPX films can transform into semicrystalline films when they are exposed to temperatures 20xc2x0 to 30xc2x0 C. above their glass transition temperature, Tg. Since re-crystallization will induce dimensional change and PPX-N and PPX-F have Tgxe2x80x2s of only about 65 and 172xc2x0 C. respectively, the amorphous or low crystalline PPX-N and PPX-F are not useful for the manufacturing of future IC""s.
Transparent semicrystalline PPX-N films have been obtained by controlling primarily the substrate temperature and chemical feed rate under a particular range of vacuum pressure in a deposition chamber. Detailed conditions and general mechanisms for making transparent semicrystalline PPX-N films have been described previously (Wunderlich et at., J. Polym. Sci. Polym. Phys. Ed., Vol. 11(1973) and Wunderlich et al., J. Polym. Sci. Polym. Phys. Ed., Vol. 13 (1975)). The suitable vacuum range is about 1 to about 100 mTorrs, preferably about 5 to about 25 mTorrs. Under this vacuum range, the crystal form and crystallinity are result directly from the feed rate and substrate temperature. Suitable substrate temperatures can range from about xe2x88x9210xc2x0 to about xe2x88x9280xc2x0 C., preferably from about xe2x88x9225xc2x0 to about xe2x88x9245xc2x0 C. During IC fabrication, wafer temperature is controlled by the cooling of an electric chuck or a wafer holder using a coolant. A wafer temperature below about xe2x88x9245xc2x0 C. is desirable for obtaining a high deposition rate, but it requires a special, expensive coolant such as fluorocarbon fluid or silicone oil.
It should be noted that at very low substrate temperatures, about xe2x88x9250xc2x0 to xe2x88x9260xc2x0 C., nucleation rates can be very high and hetero-epitaxial or highly oriented crystal growth is possible. The resulting polymer crystals would therefore be in xe2x80x9ctranscyrstallinexe2x80x9d or xe2x80x9ccolumnarxe2x80x9d forms. At these low temperature ranges, diradicals are absorbed very rapidly and the film growth rates are very high. However, this is achieved at the expense of the resulting crystallinity due to the entrapment of low molecular weight PPX-F units or other defects. A PPX-F film with low crystallinity can have poor dimensional stability at temperatures above its Tg, about 172xc2x0 C. PPX-F films prepared under these conditions thus still need to be properly annealed before they can be useful for the manufacturing of future IC""s. Thin films consisting of even more than few percent of low molecular weight PPX-F polymers are not useful due to the poor dimensional and chemical stability during the manufacturing of IC""s.
Therefore, under the vacuum range of a few mTorrs and at substrate temperatures ranging from about xe2x88x9225xc2x0 to about xe2x88x9245xc2x0 C., desirable thin films with high crystallinity can be obtained by adjusting the feed rate of the precursors. Depending on the chemistries and precursors employed for the preparation, the feed rates can be very different. For example, at a feed rate from 1 to 3 standard cubic centimeter per minutes (xe2x80x9csccmxe2x80x9d) of the monomer Brxe2x80x94CF2xe2x80x94C6H4xe2x80x94CF2xe2x80x94Br and at a substrate temperature from about xe2x88x9230xc2x0 to about xe2x88x9245xc2x0 C., crystalline PPX-F films can be obtained. When the substrate temperature is higher than about 10xc2x0 to 20xc2x0 C., nucleation is difficult due to the low adsorption of diradical intermediates. However, under very high feed or flow rates, polymer crystal growth can still be possible after an induction period to overcome primary nucleation on the substrate. PPX-F films prepared under these conditions can have high crystallinity. Even without annealing, these PPX-F films can be useful for integration into future IC""s. Furthermore, it is possible to prepare a high temperature crystal form of PPX-F at substrate temperatures above 40xc2x0-60xc2x0 C. though the deposition rate will suffer enormously.
II. Methods for Making Dimensional Stable Films
However, without proper processing conditions, even highly crystalline PPX films obtained through re-crystallization will fail when subjected to fabrication processes currently employed for making IC""s. In the IC""s that use electrically plated copper as a conductor, the required annealing temperature for the copper ranges from 300xc2x0 C. for one hour to 350xc2x0 C. for 30 minutes. Some integration processes also require a substrate temperature of 400xc2x0 C. In addition, during packaging operations of the IC""s, such as wire bonding or solder reflow, structural stability of the dielectric at temperatures as high as 300xc2x0 to 350xc2x0 C. is also required. Therefore, any useful PPX film needs to be chemical and dimensionally stable at temperatures up to 300xc2x0 to 350xc2x0 C., preferably 350xc2x0 to 400xc2x0 C. for at least 30 minutes.
DSC measurements, performed at a 10xc2x0 to 15xc2x0 C. per minute heating rate and under a nitrogen atmosphere, show a peak Tg for PPX-F around 170xc2x0 C. and an Alpha to Beta-1 irreversible crystal transformation temperature, (xe2x80x9cICTxe2x80x9d), ranging from 200xc2x0 to 290xc2x0 C. with a peak temperature, T1, around 280xc2x0 C. In addition, there are also a Beta-1 to Beta-2 reversible crystal transformation temperature (xe2x80x9cRCTxe2x80x9d), ranging from 350xc2x0 to 400xc2x0 C. with a peak T2 around 396xc2x0 C. and a melting temperature, Tm, ranging from 495xc2x0 to 512xc2x0 C. with a peak Tm around 500xc2x0 C. For comparison, the corresponding Tg, T1, T2, and Tm for PPX-N are respectively, 65xc2x0, 230xc2x0, 292xc2x0 and 430xc2x0 C. (Wunderlich et at., J. Polym. Sci. Polym. Phys. Ed., Vol. 11(1973) and Wunderlich et al., J. Polym. Sci. Polym. Phys. Ed., Vol. 13 (1975)). The Alpha to Beta-1 crystal transformation occurring at T1 is irreversible, while the Beta-1 to Beta-2 crystal transformation, at T2, is reversible for both PPX-N and PPX-F. When a crystalline PPX-N or PPX-F film is exposed to temperatures approaching its T1, polymer chains in its Alpha crystalline phase will start to reorganize and transform into a more thermally stable Beta-1 crystal phase. Once this happens, the film will never show its Alpha phase again, even by cooling the film below its T1. However, if a PPX-N or PPX-F film is cooled slowly from at or above its T2 to a temperature below its T2, the less dimensionally stable Beta-1 crystal phase will reform.
One way to maximize the dimensional stability of the PPX-N or PPX-F film is to trap the polymer chains in their most thermally stable form, the Beta-2 crystal phase, if the film is to be used or exposed to temperatures approaching T2. Then, if the film is exposed to temperatures approaching or surpassing its T2, crystal transformation cannot occur, because the film is already in its Beta-2 form. Eliminating this phase transformation ensures the dimensional stability of the film. In principle, when the film is in its Beta-2 crystal phase, its dimensional stability is still assured even at temperatures approaching 50xc2x0 to 60xc2x0 C. below its Tm. A highly crystalline (greater than 50% crystallinity) PPX-F film in a Beta-2 crystal phase can be dimensionally stable up to 450xc2x0 C. for at least 30 minutes, limited only by its chemical stability.
During integration into IC""s, two processing methods can be used to assure the dimensional stability of all polymer films that exhibit a reversible crystal transformation temperature, T2, and a crystal melting temperature, Tm.
First, the feed rate and substrate temperature can be optimized during film deposition to achieve highly crystalline films in the Beta-2 crystal phase.
By controlling the feed rate and substrate temperatures, semicrystalline films consisting of either Alpha or Beta phase crystals have been prepared (Wunderlich et al., J. Polym. Sci. Polym. Phys. Ed., Vol. 11 (1973) and Wunderlich et al., J. Polym. Sci. Polym. Phys. Ed., Vol. 13 (1975)). When the substrate temperature is lower than the melting temperature of its intermediate diradical, Tdm, and when the feed rate is low (less than 0.07 g/minute), the polymerization of crystalline diradicals can result in PPX-N films that are predominantly in the Beta crystal phase and have high crystallinity. On the another hand, when the substrate temperature is higher than the Tdm, polymerization of liquid diradicals and subsequent crystallization of polymers often results in PPX-N films that are in the Alpha crystal phase and have low crystallinity.
Second, stabilized films can be obtained by heating the films to temperatures above their T2 under inert conditions, such as under a nitrogen atmosphere or under a vacuum, and then quickly quenching the films to at least 30xc2x0 to 60xc2x0 C. below their T2. A PPX-F film that is predominantly in the Beta-2 crystal phase has been obtained by heating the film to 450xc2x0 C. for 30 minutes, then quenching the film to 330xc2x0 C. at a cooling rate of more than 50xc2x0 C./minute.
Actual polymer chain motions for solid state transition or phase transformation can start from 30xc2x0 to 60xc2x0 C. below the corresponding Tg, T1, T2 and Tm depending on the history of the films, degree of crystallinity, perfection of crystals, or the existence of various low molecular weight material in the crystalline phase (Wunderlich, Macromolecular Physics, Vol. 1-2 (1976). In fact, the Beta-1 to Beta-2 transition can start at temperatures ranging from 40 to 50xc2x0 C. below T2, (about 396xc2x0 C.) for PPX-F films. Therefore, by exposing a deposited PPX-F film to 350xc2x0 C. for one hour, the quenched PPX-F film also exhibited a high content of Beta-2 phase crystallinity. The presence of Beta-2 crystals can be verified by DSC. When a PPX-F film containing a high percentage of Beta-2 phase crystals was scanned by DSC from 25 to 510xc2x0 C. under a nitrogen atmosphere, only Tm was observed and not T1 or T2.
The maximum temperature, Tmax, which is encountered during the manufacturing of IC""s, will undoubtedly be lowered over time due to technological advancements. Improvements in copper plating chemistries and the perfection of the resulting copper films will lower the required annealing temperatures. In addition, physical vapor deposition temperatures for barrier layers or cap layers could be reduced to temperatures below 400xc2x0 C. Once this occurs, the maximum processing temperature, Tmax, can be lowered to temperatures below 350xc2x0 C., possibly as low as 325xc2x0 to 300xc2x0 C. In that case, the annealing of PPX-F films can be performed at temperatures 30xc2x0 to 50xc2x0 C. below T2 (396xc2x0 C. for PPX-F) or as low as temperatures 10xc2x0 to 20xc2x0 C. above T1 (280xc2x0 C. for PPX-F). However, the annealing should be done at a temperature equal to or higher than the Tmax for 1 to 60 minutes and preferably for 3 to 5 minutes.